This disclosure relates generally to self-assembly of nanoparticles and, more specifically, to site-specific nanoparticle self-assembly.
Self-organization methodologies have been used in bridging top-down sub-micrometer fabrication approaches with engineering at the nanometer level. One promising self-assembly approach includes strained layer epitaxy that results in self-organized quantum dots. Another promising approach involves the deposition of nanoparticles on a variety of surfaces including metals, insulators and semiconductors, such as shown schematically in FIG. 1 for CdSe and CdSe/ZnS nanoparticles on glass. This includes the layer-by-layer assembly of CdSe and CdSe/ZnS (core/shell) nanocrystals with 1,12-diaminododecane. In one report, clean substrates were then taken into a glove box and immersed for 2 minutes in an anhydrous 0.05 molar (M) THF solution of diethylzinc, followed by a 2.5 minute wash in fresh THF to remove excess diethyl zinc. Afterwards, the substrates were immersed for 2 minutes in 10−3 M THF solution of diamine followed by a 2.5 minute wash in THF. The substrates were then taken out of the glove box and mounted on an automatic slide stainer, which was programmed to repeat a dip cycle including alternative dipping with 2-2.5 minute intervals, in a dispersion of nanocrystals (NCs) (having absorbance of 0.2 at 600 nm) in chloroform and in 10−3 M THF solution of diamine, with solvent washes in between. This technique however does not result in site-specificity.
Another example of non-site-specific assembly of semiconductor nanoparticles involves the self-assembly of SiOx-coated-Si nanoparticles on a variety of substrates such as glass and metal. FIGS. 2 (a) and (b) show atomic force microscope (AFM) images of this type of thin film. FIG. 2(c) illustrates the X-ray photoelectron spectroscopy (XPS) spectrum of Si/SiOx nanoparticles deposited on a silver substrate, as compared to unoxidized, milled Si and the corresponding uncoated silver substrate. The SiOx portion appears to be about 3 to 4 nanometers (nm) thick, contributing about 52.5% of the total nanoparticle volume.
Site-specific self-assembly includes advanced recognition patterns, such as inherent in DNA-decorated nanoparticles, quantum dots, and other nano/sub-micrometer entities that attach to certain receptors on specified substrate sites. An example of site-specific self-assembly using DNA-decorated nanoparticles is schematically shown in FIG. 3. Site selectivity may also be obtained by the site-specific deposition of certain reagents that in turn permit deposition of nanoparticles onto these reagent-coated patterns. However, these techniques generally do not permit lateral size reduction of the as-deposited and/or lithographically obtained patterns.
It would be particularly advantageous if a self-assembly method permits not only the site-specific deposition of nanoparticles onto predetermined sites of a substrate but also enables reduction in the lateral size of these nanoparticle regions below the attainable limits for existing lithographic technologies.